This invention relates generally to implantable electrode leads and implantable stimulators, and more particularly to implantable defibrillation electrode leads and to implantable defibrillators.
Over the past 20 years, there has been substantial work toward developing a practical, implantable defibrillator. However, several significant problems still remain. Early conceptions of implantable defibrillators, such as disclosed in U.S. Pat. No. R. 27,652 by Mirowski et al., envision a system employing a ventricular endocardial electrode and a plate electrode, mounted directly to the heat, subcutaneously, or applied to the skin. However, it was recognized early on that a totally transvenous system would be desirable in order to simplify the use of implantable defibrillators. One such system is suggested in U.S. Pat. No. 3,942,536 by Mirowski et al., which discloses a transvenous lead having electrodes intended for location in the right ventricular apex and superior vena cava. Such systems were eventually tested in human beings with some success. However, currently available commercial versions of implantable defibrillators generally employ epicardial patch electrodes alone or in conjunction with transvenous electrodes.
While systems employing epicardial patch electrodes are workable, a thoracotomy is required in order to apply the epicardial electrode or electrodes. It is generally believed that it would be highly desirable to produce an implantable defibrillator which would entirely avoid the necessity of a thoracotomy, and there has been substantial work directed toward such systems, as disclosed in U.S. Pat. No. 4,727,877 issued to Kallok and U.S. Pat. No. 4,708,145 issued to Tacker et al. Both Tacker et al. and the Kallok patents disclose the use of a transvenous, two-electrode lead in combination with a subcutaneous patch electrode.
Transvenous ventricular defibrillation electrodes are also shown in the above-cited Mirowski patents and in the Tacker and Kallok patents cited above. Other endocardial defibrillation electrodes are disclosed in U.S. Pat. No. 4,481,953 issued to Gold et al., U.S. Pat. No. 4,161,952 issued to Kinney et al., and U.S. Pat. No. 4,641,656 issued to Smits. The Kinney, Smits and Kallok patents also disclose transvenous defibrillation electrodes intended for use in or adjacent to the coronary sinus.
U.S. Pat. No. 4,392,407 issued to Williams et al. and co-pending, commonly assigned application Ser. No. 284,957 by Mehra and Ser. No. 284,955 by Bardy, both filed Dec. 15, 1988 disclose multiple electrode systems employing subcutaneous patch electrodes, coronary sinus/great vein electrodes, and ventricular endocardial electrodes.
U.S. Pat. No. 4,355,646 issued to Kallok shows endocardial defibrillation leads employing multiple electrodes for location in the right ventricle, each of the electrodes being coupled to a different electrical connector. In use, the ventricular electrodes of the Kallok lead are coupled together during delivery of a defibrillation pulse, and the pulse is delivered between the paired ventricular electrodes and corresponding pair of electrodes located in the superior vena cava. This is the same endocardial electrode system as disclosed in the above-cited Tacker patent. A similar electrode lead is disclosed in U.S. Pat. No. 4,291,699 issued to Geddes et al., in which the two ventricular electrodes are tied together during delivery of a defibrillation pulse, and also used for sensing impedance of the blood within the ventricle. Yet another use of a lead as disclosed in the Kallok et al. patent is set forth in U.S. Pat. No. 4,499,907, which employs the two ventricular electrodes coupled together during delivery of a defibrillation pulse, and also employs the two ventricular electrodes as bipolar pair for sensing the electrical signals indicative of heart contractions, in the fashion of a normal, bipolar pacemaker.
An additional multi-electrode ventricular defibrillation lead is disclosed in U.S. Pat. No. 3,857,398 issued to Rubin. The two ventricular electrodes in the Rubin lead are employed for ventricular pacing and sensing of heart beats. One of the ventricular electrodes is used in conjunction with an atrial electrode for delivery of defibrillation pulses.